Viral single standed RNA is sensed by cells via toll-like receptor (TLR)-7 and TLR-8. We have recently shown that stimulating TLR-7 and TLR-8 relaxes airway smooth muscle and prevents broncho-constriction in response to a variety of stimuli. The effect is profound, and can lead to virtually complete relaxation of smooth muscle. We have demonstrated this effect in guinea pigs and mice, and in human airway tissues. TLR7 dependent broncho-dilation in guinea pigs and in human airways is mediated by production of nitric oxide, while TLR8 dependent broncho-dilation is not. Our preliminary data suggest that TLR8 mediated broncho-dilation is mediated by production of prostaglandins and opening of the large conductance, calcium activated potassium channel. We have also shown that both antigen sensitization and acute viral infection substantially impair TLR- dependent broncho-dilation. In this application, we propose three specific aims: Specific Aim #1. To A) use TLR7(-/-) mice, as well as newly generated TLR8(-/-) and TLR7(-/-)TLR8(-/-) mice, to more thoroughly investigate and establish the signaling pathways responsible for the effects of these receptors on airway neurons and smooth muscle, B) test whether these receptors signal through nitric oxide, prostaglandins, and the large conductance, calcium activated potassium channel (BKCa) in human airways in vitro, and C) explore the role of nitric oxide and prostaglandins and changes in intracellular calcium in rapid signaling by these receptors in primary cultures of human airway parasympathetic neurons and airway smooth muscle cells. Specific Aim 2: To test whether decreased TLR mediated broncho-dilation after antigen sensitization is mediated by decreased TLR7 and/or TLR8, testing signaling pathways in airway smooth muscle identified in Aim #1. Since these TLRs are on parasympathetic nerves, as well as on eosinophils recruited to the airway nerves, we will also test whether TLR7 and TLR8 change neural control in sensitized airways. SPECIFIC AIM #3: To test whether decreased TLR mediated broncho-dilation after viral infection is mediated by decreased TLR7 and/or TLR8 pathways, testing all second messenger signaling pathways in airway smooth muscle identified in aim one. We will also investigate the role of changes in parasympathetic function. The results of the experiments we propose will be important in establishing the potential of TLR7 AND TLR8 agonists as treatments for asthma and other airway diseases. In addition, because these receptors respond to viral RNA, understanding the effects of stimulating TLR7 receptors in the airways, as well as the loss of these effects in models of asthma, will help us understand the pathophysiology of virus induced asthma attacks.